A continuing demand exists for a simple, inexpensive method and apparatus which can be used to vent marine outdrive units, and which can also be used to monitor and insure adequate oil supply to marine outdrive units. In particular, a need exists for a simple, inexpensive system to enable a marine outdrive to utilize a pressure equalization vent to eliminate the slight positive pressure which occurs by the heating of a marine outdrive unit during operation, and to eliminate the slight negative pressure which occurs in a marine outdrive unit upon cooling after operation. Also, it would be desirable for a boat operator to be able to visually check the outdrive oil system to be sure that (a) sufficient oil is in the system, and (b) that the oil is of the desired quality, and has not become contaminated or emulsified by water or other foreign substance.
The need for such devices is commonly seen in conjunction with the use of marine outdrive units, where it is desirable to (a) prevent corrosive saline water from being sucked into a cooling outdrive unit after the use of same, and (b) to conveniently monitor the oil level while the unit is operating. Currently, it is difficult or impossible to monitor the oil level in marine outdrives while operating the unit. As a result, there are concomitant adverse effects on outdrive service life and on outdrive unit maintenance costs.
For example, I have inadvertently damaged several outdrive units on a commercial fishing boat that I own by catching trolling wire in the prop and ruining the seal around the output shaft. In systems such as those manufactured by Volvo and some other manufacturers, there is no way to check the oil level for so long as the outdrive unit is in the water. Thus, I had no warning that the oil level was running low, and did not discover the loss of oil from the outdrive gear system until after operation had occurred without benefit of lubrication. Consequently, expensive repairs were necessary.
It should also be noted that a failure of critical outdrive unit seals can also be the result of normal wear and tear, or by operating for extended periods of time with dirty oil (for example, contaminated with metal flakes), or by striking submerged objects with the prop. In a few cases, oil may be lost immediately and the danger created of unit operation without lubrication.
Most outdrive units have oil levels which do not completely fill the upper shell of the outdrive, so as to allow for expansion of the oil during operation. In some models, a gimble bearing which supports the upper gear set is located above the normal oil level, and is lubricated by splash from gears during operation. Even if no immediate problem occurs due to the aforementioned damage to seals, when the outdrive cools after normal operation, the vapor space in the top of most outdrive units tends to create a vacuum, which draws saline waters into the outdrive unit through any damaged or leaky seals. Thereafter, once the unit cools, loss of oil may occur through leaky seals. Thus, many outdrive units are damaged while sitting in the marina between periods of service.
Another condition adverse to extended outdrive unit service life is that cooling of moist air within the outdrive vapor space causes condensation to form within the cap and on the upper gear set bearing. The ensuing rust may cause premature failure of the bearing, and contributes to wear rates and reduced service life of the gears and the seals.
In addition, since most factory built outdrive systems lack a vent system, outdrive units have a moderate amount of internal pressure build-up due to oil expansion caused by higher oil temperatures which are experienced during high speed operations. This tends to force oil outward through the oil seals which seal oil in and water out, and such leakage may occur through damaged or weak seals.
Another common deficiency of the heretofore available oil systems for outdrive units is the absence of a readily apparent visual indication to the operator that an adequate supply of suitable oil is available to the outdrive unit. The advantage which would be provided by such an indication is important and self-evident.